(A) Field of the Invention
The present invention relates to a portable blackbody furnace with high temperature stability and uniformity, and more particularly, to a portable blackbody furnace with temperature high stability and uniformity, which is suitable for the temperature calibration of radiation thermometers.
(B) Description of the Related Art
FIG. 1 is a cross-sectional diagram of a conventional blackbody furnace 10 for the temperature calibration of radiation thermometers. The blackbody furnace 10 comprises a metallic sheet 20, a heater 22, and a plurality of thermometers 24, wherein the metallic sheet 20 forms an internal cavity 14 with an opening 16. The space between the metallic sheet 20 and the shell 28 is filled with insulation material 26 to avoid heat loss. During the temperature calibration process, the metallic sheet 20 is heated to a predetermined temperature such as 38° C. by the heaters 22, the probe head of the radiation thermometer is positioned into the internal cavity 14 in the metallic sheet 20 through the opening 16 to detect the temperature of the internal cavity 14, and the detected temperature is used as a standard temperature to calibrate the radiation thermometer.
The metallic sheet 20 is used to form the internal cavity 14, and the temperature of the metallic sheet 20 is controlled primarily by a controller (not shown in the drawings) via the heater 22. However, during the temperature calibration of the radiation thermometer, a portion of heat emits from the blackbody furnace 10 via the opening 16 and the radiation thermometer also captures heat from the internal cavity 14, which results in a dramatic decrease of the temperature in internal the cavity 14. In other words, the temperature uniformity and stability in the internal cavity 14 are poor, and the correctness of the temperature calibration is easily to be influenced. As a result, the blackbody furnace 10 must be incorporated with a high precise controller to ensure the temperature stability in the internal cavity 14, and the precise controller dramatically increases the total cost.
FIG. 2 is a cross-sectional diagram of another conventional blackbody furnace 50. The blackbody furnace 50 comprises a metallic sheet 60 with a thickness about 2 millimeters and a shielding plate 52, wherein the metallic sheet 60 forms an internal cavity 54. During the temperature calibration process, the blackbody furnace 50 is immersed to a predetermined level 62 in a tank that is filled with liquid such as water or oil and maintained at a constant temperature, and the probe head of the radiation thermometer is positioned into the internal cavity 54 via an opening 56 to detect the temperature in the internal cavity 54. Particularly, the blackbody furnace 50 uses the liquid with a great amount of heat capacity in the tank to decrease the heat loss during the temperature calibration of the radiation thermometer so at to ensure the temperature stability. However, the volume and weight of the blackbody furnace 50 is very huge and weighty, which is not suitable to be portable.